Tracheal gas insufflation as a lung-protective strategy: Physiologic, histologic, and biochemical markers

Objective: Conventional mechanical ventilation in acute lung failure potentiates lung injury, which can be assessed by physiologic, histologic, and biochemical markers. Thus, new ventilation strategies are directed at reducing lung injury. Tracheal gas insufflation has been shown to reduce endotracheal tube prosthetic deadspace and peak inspiratory pressure during conventional mechanical ventilation. Our objective was to use physiologic, histologic, and biochemical markers to test the hypothesis that tracheal gas insufflation in acute lung injury is lung protective. Design: Animal experiment. Setting: University setting. Subjects: Juvenile rabbits (n = 12; 1.95 ± 0.1 SE kg). Interventions: Rabbits were anesthetized, instrumented, paralyzed, and ventilated with F_IO2 = 1.0. Lung injury was induced with repeated saline lavage (10 mL/kg per lavage until Pa_O2 ≤150 mm Hg and compliance ≤0.50 mL/cm H₂O/kg for 30 mins). Animals were randomized to conventional mechanical ventilation with and without 0.5 lpm of continuous tracheal gas insufflation (Vygon endotracheal tube) for 4 hrs to maintain Pa_CO2 at 45-55 mm Hg by adjusting the peak inspiratory pressure; other conventional mechanical ventilation settings remained constant. Measurements and Main Results: Gas exchange and pulmonary mechanics were measured every 30 mins; plasma and pulmonary tissue were taken for cytokine and histologic evaluation after 4 hrs. Peak inspiratory pressure, tidal volume, and physiologic deadspace were significantly less (p < .05) in the tracheal gas insufflation animals when compared with conventional mechanical ventilation animals. Pa_O2, positive end-expiratory pressure, mean airway pressure, vital signs, Pa_CO2, and respiratory resistance and compliance were not statistically different between the two groups. There was a difference (p < .05) in interleukin-8 tissue (pg/μg protein; dependent = 52.4 ± 7.6 vs. nondependent = 32.8 ± 4.2) and plasma levels (pg/mL; preinjury = 7.2 ± 2.3 vs. postinjury = 118 ± 58). Histology showed a trend toward protection of alveolar structures for tracheal gas insufflation. Conclusions: Tracheal gas insufflation resulted in lower ventilatory requirements (peak inspiratory pressure, tidal volume, and deadspace) and a more favorable histologic trend than conventional mechanical ventilation. Tracheal gas insufflation offers potential as a lung-protective strategy for acute lung injury in the developing rabbit lung and may be a useful clinical adjunct to neonatal respiratory management.